Loss of memory for the characteristics of stimuli (i.e., forgetting of stimulus attributes) can lead to increases in behavior, a consequence quite different from the impairments associated with the forgetting of responses. Evidence from animal and human research for the forgetting of stimuli as a distinct memory principle is presented, and the methodological and conceptual implications of this pervasive type of memory loss are considered. Malleability of eyewitness memory, cognitive confusions, sleeper and familiarity effects, and temporal distortions in inferences and attributions are among the varied behavioral phenomena that can be accounted for in terms of forgetting of stimulus attributes.